Transition metal dichalcogenides (TMDs) are claimed to absorb between 5% and 10% of the incident sunlight when exfoliated into thicknesses inferior to 1 nm displaying one order of magnitude higher sunlight absorption than most of the commonly used solar absorbers. In monolayers this leads to the observation of unique optical and optoelectronic properties. Pronounced photoconducting and photovoltaic responses are also observed in heterostructures incorporating graphene and multilayered TMDs.
The high light absorption in TMDs is attributed to the existence of pronounced van Hove singularities in the electronic density of states leading to a pronounced joint density of states in the visible light region and hence ensuring relatively strong light-matter interactions. Strong light matter interactions led to reports of incredibly high photoresponsivities in single-layer MoS2, i.e., approaching ˜103 A W−1 in the limit of very low illumination power densities. For a large area, chemical vapor deposited heterostructures of graphene onto MoS2 monolayers photoresponsivities as high as 107 A W−1 have been reported under illumination power densities p approaching just ˜10−3 Wm−2. Very high photoresponsivities and concomitantly high external quantum efficiencies have also been observed for graphene and transition metal dichalcogenides (TMD) based heterostructures, even when transferred on to flexible substrates.
Various methods are known in the art for harvesting a photovoltaic response from these thin layers of transition metal dichalcogenides, including the formation of p-n junctions, and vertical heterostructures. While many of these approaches have led to sizeable short-circuit currents or currents in the absence of a bias voltage resulting from the photovoltaic effect, the conversion efficiencies of these TMD based devices are still unacceptable for technological applications.
Accordingly, what is needed in the art is a transition metal dichalcogenides (TMD) based device that exhibits a higher extracted photovoltaic power conversion efficiency than TMD-based devices currently known in the art.